304 Prof. J. Joly on the Apophorometer. 



off as S0 2 . On the formula the weights should be Ag = 7*4 ; 

 As = 1*7 ; S = 2*2. In Nature considerable departures from 

 the theoretic proportions occur in substances such as the 

 above. 



Niccolite. ..Ni As. Ni43*9; As56*l. Weight taken 26*5 mgrms* 



At a sub-red heat a white sublimate of As 4 6 was formed.. 

 Weight 16*7 mgrms. This contains 12*7 mgrms. of As, and, 

 by difference, Ni=13'8. On the formula As = 14*8 and 

 Ni = ll-7. 



In this experiment the precaution of reheating was not at 

 first carried out. The result shows a deficiency of As, and 

 it was afterwards found that more sublimate was obtainable 

 from the residue. A fresh experiment was made : — 



Niccolite, as above : weight taken 30 mgrms. 



(1) Raised to dull red ; weight of sublimate obtained 

 22'1 mgrms. (2) No further sublimate formed. 



From this As = 16'7 mgrms., and, by difference, Ni = 13*3 

 mgrms. From the formula the quantities should be As = 16*8 ; 

 Ni = 13'2. 



Sylvanite. (An, Ag) Te 2 . Ag 13*4 ; Au 24\5 ; Te 62'1. 

 Weight taken 9*2 mgrms. 



(1) At a sub-red heat a grey-black sublimate formed : 

 weight 1*4 mgrms. The temperature was now raised to full 

 red, when a copious sublimate of a white colour came off. 

 Weight 4*9 mgrms. No further sublimate was obtainable 

 up to an orange-yellow heat. 



There can be little doubt that the iron-black sublimate is 

 the monoxide TeO, and that the white sublimate is the 

 dioxide Te0 2 . On this view 5*3 mgrms. of Te have been 

 obtained. By difference (Au, Ag) = 3*9 mgrms. The formula 

 affords Te = 5'6 ; (Au, Ag) = 3'6 when Au : Ag = l : 1. 



This experiment suggests that a part of the Te is more 

 loosely combined than the rest, and hence passes into that 

 oxide which is formed at the low temperature. It may be 

 that this part is associated with one of the two metallic 

 elements present. The proportions in which Ag and Au 

 occur in sylvanite vary considerably; the goldibeing, however r 

 always predominant in weight. This would imply that a 

 selenide of silver represented the more unstable body. Some 

 confirmation of this is found in the fact that at the conclusion 

 of the first heating the appearance of the residue suggested 

 the complete separation of the metallic silver ; there was less 

 evidence for the separation of gold. At the conclusion of 



